Circular  No.  1 16. 


United  States  Department 

BUREAU    OF   ENTOM 
L.   O.   HOWARD,   Entomologist  and 


THK  LARGEB  CORN  STALKS 

i  Diatrcea  saccharalis  Fab. » 

By   <il  OBGI     l  i.    AlNSLIE, 

Associah    Professor  of   Entomology,   Clemson     Igricultural   College   of   South 

Carolina. 

INTRODI  CTION. 

In  many  southern  cornfields  a  heavy  wind  late'in  the  season,  be- 
fore the  corn  is  matured,  doe-  great  damage  by  breaking  the  plants 
off  at  the  surface  of 
the  ground,  thus 
ruining  them.  An 
exaininal  ion  of  i  hese 
broken  stems  will,  in 
most  cases,  show  that 
t  h  ey  have  b ee n 
greatly  weakened  by 
the  burrows  of  a 
larva  or  caterpillar. 
Tin-  larva  (  fig.  1 )  is 
known  a-  "the  lar- 
ger corn  stalk-borer  " 
{/>/',//,<>  lara- 

lis).  It-  work  is 
largely  within  the 
stem  of  the  plant  and 
i-  so  concealed  that. 
in  most  cases,  unless  weather  condition-  make  it  conspicuous,  the 
presence  of  the  insect  passes  unnoticed. 


Pio.  1.  -The  larger  corn  stalk-borer  \l>i'it,<i<i  saccharalis)  : 
a.  Summer  form  of  larva  :  h,  • ,  hibernating  forms  of 
larva;;  •/.  third   thora  nenl    from  above;  e,  eighth 

abdomlna  I    si  gmi  at    I  t>  >m    aboi  e ;    f,   abdominal    s< 
from   1  from  side.    ■/.  >>,  c,  Enlarged;  d,  <.  f. 

still  more  enlarged.     (Redrawn  from  Howard  1 


"This  i.s  pra.'ticnlly  :i  revision  of  Circular  No.  16,  prepared  many  years 
aqp  by  It.  1..  < ».  Howard.  .Mr.  Alnslle  was  formerly  in  the  employ  of  this 
Bureau  as  an  agenl  and  expert  in  cereal  and  forage  insed  investigations,  ami 
this  pesl  was  "in'  of  the  subjects  >•(  investigation  assigned  to  him.  He  after- 
wards ■  1  i « 1  some  work  upon  the  s|ie,irs  for  the  South  Carolina  Agricultural 
Experiment  Station  in  cooperation  with  this  Bureau. 
2 1 7:;  1  -NO.  lie.     LO 


This  insect  seems  to  have  been  originally  an  enemy  of  sugar  cane 
and  to  have  first  transferred  its  attention  to  corn  in  the  southern 
part  of  this  country,  where  corn  and  cane  are  grown  over  the  same 
territory.  It  occurs  in  many  countries  where  sugar  cane  is  the  staple 
crop,  and  has  caused  great  damage  in  the  West  Indies,  British  Guiana, 
Australia,  and  Java.  The  bulk  of  the  evidence  goes  to  show  that  it 
was  first  brought  into  this  country  with  the  importation  of  sugar- 
cane cuttings  from  the  West  Indies  and  Central  and  South  America, 
where,  since  early  times,  it  has  interfered  with  the  production  of  this 
staple. 

In  the  United  States  this  borer  is  found  almost  universally  through- 
out the  South,  from  Maryland  to  Louisiana  and  westward  to  Kansas. 
Among  other  localities  it  has  been  reported  to  the  Bureau  of  Ento- 
mology from  Bennettsville,  S.  C,  as  destroying  corn,  especially  that- 
planted  early  in  the  season.  From  Waynesboro,  Ga.,  in  1909,  reports 
were  received  that  in  some  fields  the  corn  was  "  at  least  one-third 
destroyed  "  by  an  insect  which  later  proved  to  be  this  species.  In 
Virginia  it  has  been  found  recently  at  Nathalie,  where  it  was  studied 
by  Mr.  J.  A.  Hyslop,  of  this  Bureau,  at  Allenslevel,  at  Church  Road, 
and  at  Farmville.  In  late  October,  1909,  Mr.  E.  G.  Smyth  found 
that  nearly  one-half  of  the  cornstalks  at  Diamond  Springs,  Va., 
were  infested,  often  as  many  as  three  larva1  being  found  in  one 
stalk,  boring  from  the  surface  of  the  ground  clown  to  the  base  of 
the  root;  and  while  the  author  has  frequently  found  as  many  as 
a  dozen  larvae  in  a  single  stalk,  there  are  never  more  than  two  or 
three  pupse  in  the  same  stalk.  In  each  case  it  had  damaged  the  corn. 
and  especially  that  planted  early  in  the  season.  Detailed  investi- 
gations of  this  insect  have  been  conducted  by  the  author  during  the 
last  two  years,  chiefly  in  South  Carolina. 

NATURE  OF  DAMAGE. 

Corn  is  damaged  by  these  caterpillars  in  two  ways.  First,  in  the 
early  part  of  the  season,  while  the  plants  are  small,  they  work  in  the 
"  throat "  of  the  young  corn,  and  if  the  tender  growing  tip  within 
the  protecting  leaves  is  once  damaged  all  chances  that  the  plant 
will  become  a  normal  productive  specimen  are  gone.  In  many  sec- 
tions of  the  South  this  is  commonly  known  as  "  bud- worm  "  injury, 
and  though  there  are  several  other  insects  which  cause  a  similar 
mutilation  of  the  leaf,  a  very  large  proportion  of  the  so-called  "  bud- 
worm  "  damage  may  be  charged  to  this  insect.  The  effect  of  its 
work  on  the  leaves  of  the  young  corn  plants  is  similar  to  that  re- 
sulting from  attacks  by  the  corn  billbugs  (Sphenophonis  spp.)  and 
is  evidenced  by  the  familiar  rows  of  small  circular  or  irregular  holes 
across  the  I 'lades  of  the  plant   (fig.  2). 

The  other  form  of  serious  damage  chargeable  to  this  pest  occurs 
later  in  the  season.  The  larva',  having  then  left  the  leaves  and 
[Cir.  i  16] 


descended  to  the  lower  part  of  the  stalk,  tunnel  in  the  pith.  (See 
fig.  3.)  If  the  larvae  are  at  all  numerous  in  the  stalk,  their  burrows 
so  weaken  the  plant  thai  any  unusual  strain  will  lay  it  low  and 
destroy  all  chance  of  its  maturing.  While  frequently  ten  or  more 
larvae  may  live  and  mature  in  one  plant,  it  musi  be  remembered  that 


Pig    2.  —  Work  of  larger  corn  stalk-borer,  mutilation  of  leaves  of  corn  bj    larvse. 

Great]     reduced       (<  Original.) 

any  infestation,  however  light,  will  lessen  in  some  degree  the  vitality 
of  the  plant  and  cause  a  corresponding  loss  in  the  quality  and  quan- 
tity of  the  harvest. 

HABITS    OF    THE    I.Ai;\  .11. 

[mmediately  upon  leaving  the  egg  in  spring,  the  young  larva  of 
the  first  generation,  spinning  a  silken  thread  behind  it,  wander- 
down  into  the  throat  of  the  plant  as  far  as  the  water  or  dew  usually 
standing  there  will  allow  it  to  go,  and  begins  to  (rcA  on  the  leaves, 
g  back  and  forth  through  the  yet  unfolded  clusters  and  -non 
riddling  the  more  tender  leaves  with  aimless  burrows.  If  the  bur- 
row reaches  the  tender  terminal  bud  where  the  future  joint-  are 
being  formed,  further  growth  at  that  point  ceases  and  the  plant  he- 
come-  stunted  and  misshapen,  with  no  tassel,  ks  the  plant  continues 
to  mature,  the  larva  "grows  out."  as  the  farmer-  say.  It  i-  more 
LClr.  1 16] 


likely  that  it  is  the  evidences  of  its  work  and  not  the  larva  itself 
that  "grow  out;"  but  for  whatever  reason,  the  caterpillar  soon  leaves 
the  more  leafy  portion  of  the  plant  and  attacks  the  stalk  at  or  near 
the  ground.  Here  a  hole  is  cut  through  the  outer  wall  of  the  stalk 
and  the  larva  burrows  upward  for  a  short  distance,  after  which  it 
seems  to  run  aimlessly  through  the  pith,  frequently  even  leaving  the 


PIG.   :'.. — The  larger  corn  stalk-borer:   Larva   in   lower   part   of  com   plant    preparatory   to 
hibernation.     Reduced.     (Original.) 

stalk  entirely  and  reentering  it  at  another  point.  Tinning  upward, 
the  caterpillar,  when  fully  grown,  bores  toward  the  outside  and 
cuts  a  circular  hole  in  the  outer  wall  of  the  stalk.  Then,  after 
spinning  a  few  loose  threads  across  this  opening  to  keep  out  un- 
desirable visitors,  it  retreats  a  short  distance,  plugs  the  burrow  below 
with  digested  pith,  and  in  the  chamber  thus  created  slowly  changes 
to  the  next  or  pupal  stage  (fig.  4,  c). 
[Cir.  no] 


Seldom  is  the  stalk  damaged  above  the  third  joint  from  the  ground, 
although  the  larvae,  when  small,  arc  found  in  the  large  midribs  of 
the  lower  leaves  and  later  in  the  season,  when  the  food  suppl}'  is 
restricted,  even  in  succulent  nubbins  farther  up.  They  sometimes 
also  penetrate  the  underground  pari  of  the  stalk  in  feeding  and  enter 
some  of  the  larger  brace  roots  for  a  shorl  distance. 

The  larvae  of  the  second  general  ion  work  in  a  similar  manner,  except 
that  at  the  time  they  appear  the  tassel  has  been  formed;  hence  the 
damage  is  now  confined  altogether  to  the  lower  stalk.  Thus,  instead 
of  arranging  to  pass  the  pupal  stage  in  the  upper  stalk,  they  pene- 
trate to  the  rool   to  hiber 


nate  and  there,  as  larva?, 
pass  the  w  inter  in  a  qui- 
escent state  (  fig.  3). 

SI   \-"N  \i.    HISTORY. 

During  the  winter  this 
enemy  of  corn  is  to  be 
found  as  a  robust,  creamy- 
white  larva  of  the  second 
generation  in  the  lower 
part  of  the  stalk — or  of 
the  stubble,  if.  a-  i-  usu- 
ally the  case,  the  corn 
has  been  cut.  In  this  lo- 
cation the  larva  form-  a 
small  ea\  it  v  below  t he  sur- 


b 

Fig.  I.  The  larger  corn  stalk-borer:  </.  Female 
moth  :  b.  wings  hi'  male  :  i  .  pupa.  All  sum.  what 
enlarged,      i  Original.  > 


face  of  the  ground,  well  protected  from  birds,  predaceous  insects, 
and  unfavorable  weather  condition-.  From  the  time  the  corn  is 
mature  in  the  fall  until  ahoui  corn-planting  time  in  the  spring  this 
caterpillar  remain-  inactive.  About  the  time  the  ground  i-  being 
prepared  for  corn,  from  March  1.".  to  April  30,  depending  on  the 
locality,  this  larva  changes  into  a  reddish-brown  pupa  or  chrysalis 
(fig.  I.  >) .  A  ft  ei'  a  further  period  of  ten  or  more  da\  -"  inactivity  the 
adult  in-ect  emerges  from  the  pupa  case  as  a  pale  brownish-yellow 
moth  (fig.  t,  a,  6 ), with  a  spread  of  wings  of  about  an  inch  and  a  quarter. 
The  moth-  then  mate  and  the  female-  begin  at  once  to  deposit  eggs 
on  the  underside  of  the  leave-,  the  larv;e  hatching  from  these  eggs 
forming  the  first  generation. 

The  eggs  hatch  in  from  seven  to  ten  days  and  the  young  larva? 
begin  their  destructive  work  in  the  upper  leafy  portion  of  the  plant, 
later  descending  to  the  base  of  the  -talk,  where  they  attain  full 
growth.  This  period,  from  egg  to  full  grown  larva,  requires  from 
twenty  to  thirty  days,  depending  largely  on  the  weather  conditions 

[Clr.  1 16] 


and  the  vigor  of  the  plant.  The  larva1  when  full  grown  pupate  in 
the  stalk,  usually  in  the  second  or  third  joint  from  the  ground,  and 
in  from  seven  to  ten  days  the  adult  moths  of  the  first  generation 
emerge. 

The  eggs  for  the  second  generation  are  laid  in  similar  positions 
on  the  lower  leaves  or  on  the  stem,  and  the  larva1,  after  feeding  for 
a  short  time  on  the  leaves,  go  directly  to  work  in  the  stalk,  completing 
their  larval  growth  in  the  pith  of  the  lower  stalk  as  did  the  larva; 
of  the  first  generation.  No  damage  is  done  to  the  upper  part  of  the 
plant  by  larvae  of  the  second  generation. 

By  the  time  the  larva?  of  the  second  generation  are  full  grown 
the  corn  is  rapidly  nearing  maturity,  and,  instead  of  pupating  in 
the  stalk,  they  turn  downward,  penetrate  to  the  extreme  lower  tip 
of  the  taproot,  and  there  form  a  small  cavity  in  which  to  pass  the 
winter.  At  this  time  the  larva?  lose  the  darker  markings  of  the  ear- 
lier forms,  and  as  overwintering  larva?  are  creamy-yellow  in  color. 
They  are  plump  and  active  in  the  fall,  but  flabby  and  sluggish  after 
fasting  throughout  the  winter.  The  only  way  in  which  the  insect 
passes  the  winter  is  in  the  form  of  this  overwintering  larva,  found 
below  the  ground  in  the  extreme  lower  tip  of  the  corn  roots.  Two 
generations  a  }rear  aj^pear  to  be  the  rule,  although  it  is  possible  that 
in  the  far  South  and  on  sugar  cane  a  partial  third  generation  may 
occur. 

DESCRIPTIONS. 

Egg. — The  eggs  are  flat  and  scalelike,  almost  circular  in  outline, 
and  are  placed  in  rows  or  irregularly,  overlapping  one  another 
shingle  fashion.  From  two  to  twenty-five  eggs  are  laid  in  one  place 
on  the  underside  of  a  lower  leaf  or  occasionally  on  the  upper  side 
and  on  the  stem.  Creamy-white  when  first  laid,  they  gradually 
change  to  a  reddish-brown,  and  in  seven  to  ten  days  a  minute,  bristly, 
reddish  caterpillar  cracks  the  shell  and  crawls  out  through  a  narrow 
slit  at  one  end.  The  eggs  are  about  three  one-hundredths  of  an  inch 
(7.G  mm.)  long  and  about  two-thirds  as  wide.  After  hatching,  the 
white  papery  shells  are  soon  washed  off  the  leaves. 

Larva. — The  larva  of  the  first  generation  (fig.  1.  a)  when  full 
grown  is  a  robust,  dirty-white  caterpillar  1  inch  in  length,  thickly 
covered  with  round  or  irregular  dark  spots,  each  of  which  bears  a 
short,  dark  bristle.  When  the  larva  is  small  these  markings  are 
almost  contiguous,  giving  the  whole  insect  a  dark  color  and  a  hairy 
appearance.  The  head  and  thoracic  plate  of  all  the  stages  are 
brownish-yellow.  The  overwintering  larva  of  the  second  generation 
(fig.  1,  6,  c)  gradually  loses  the  darker  markings  of  the  body  and 
after  the  last  molt  remains  unspotted  and  light  yellow  in  color. 
excepl  for  the  head  and  the  thoracic  plate,  which  retain  the  brownish- 
yellow  of  the  earlier  stages. 
[CIr.  i  nil 


Pupa.  -When  first  formed,  the  pupa  (fig.  l.  -  I  is  light  honey- 
yellow  in  color,  soon  changing  to  a  rich  mahogany-brown.  Ii  is 
about  seven-eighths  of  an  inch  in  length  and  is  able  to  contorl  itself 
violently  when  disturbed.  It  lies  in  the  cavity  usually  with  the  head 
up.  On  emerging,  the  moth  leaves  the  brownish  shell  of  the  pupa 
case,  partially  withdrawn   from  the  hole. 

Adult.  The  female  moth  (fig.  I.  a)  varies  in  color  from  almost 
while  to  Smoky  yellow.  The  fore  wings,  which  spread  to  ahoin  l  ; 
inches,  are  darker  than  the  hind,  wings,  and  bear  faint  markings. 
When  at  res!  the  wine-  are  held  close  to  the  body,  forming  an  acute 
triangle.  The  c«r<r  hiving  is  done  for  the  most  pari  either  at  night  or 
in  the  dusk  of  evening,  the  moths  flying  rapidly  from  plant  to  plant. 
The  male  moth  (lie'.  1.  I> )  is  usually  somewhat  darker  in  color  than 
the  female  and  always  -.mailer. 

FOOD  PLANTS. 

Besides  corn  and  sugar  cane,  this  borer  has  been  reported  as  feed- 
ing on  sorghum,  Johnson  grass,  guinea  corn,  and  grama  grass.  The 
injury  to  the  four  last-mentioned  plant-  is  never  severe,  but  in  plan- 
ning methods  of  control  they  must  be  considered  and  an  examination 
mad.'  to  determine  whether  or  not  they  are  harboring  the  pest. 

\  ATI  i;  w.  (  iin  KS. 

The  larger  corn  stalk-borer  has  very  few  natural  enemies.  A 
minute  Ilynicnopterous  parasite  i  I  richogramma  pretiosa  Rilej  )  has 
in  a  very  few  instances  been  found  living  in  and  destroying  the  eggs. 
In  one  case  ten  of  these  minute  parasites  were  reared  from  two  eggs. 
The  larva  of  a  In-own.  velvety  beetle  {Chauliognathm  pennsylvanicus 
DeG.)  sometimes  enter-  the  hole-  in  the  stalks  of  stubble  after  the 
corn  i-  cut  and  devours  the  caterpillars  found  therein.  This  larva 
has  been  found  to  be  <d'  greal  value  in  reducing  the  numbers  of  the 
borers  in  fields  of  sugar  cane.  The  termite-  or  white  ants  (Termes 
jinr'/p,  Koll.i.  locally  known  a-  "wood  lice,"  have  been  observed 
destroying  the  larvae  in  the  stubble  in  the  winter,  although  apparently 
only  when  the  presence  of  the  larvse  interfered  with  the  work  of  the 
ants.  In  a  few  cases  bodies  of  the  borers  have  been  found  in  the 
stubble  killed  by  a  fungus,  as  yet  undetermined,  which  envelops  their 
bodies  in  a  white  mold.  Fungi,  however,  are  too  dependent  on 
weather  conditions  to  be  of  any  practical  value  in  controlling  the  pest. 

PREVENTIVE     Ml   V.S1   RES. 

Rotation  is  one  of  the  best  general  preventives  of  injury  from  in- 
sects affecting  field  crop-.  Experience  has  shown  that  win  re  corn 
has  followed  itself  upon  the  same  field  for  two  or  more  years  there 
has  been  a  much  greater  loss  from  the  borer  than  where  an  annual 
change   of  crop  has  been   practiced.     This   i-  especially   noticeable 

[Cir.  l  L6] 


8 

■where  stalks  or  stubble  from  the  previous  year  have  been  allowed  to 
remain  undisturbed  throughout  the  winter.  The  moths,  upon  emer- 
gence in  the  spring,  finding  themselves  surrounded  by  tbe  young 
corn,  commence  egg  laying  at  once  and  escape  the  clangers  encountered 
in  searching  for  another  field  of  corn.  A  forced  journey  in  search  of 
young  corn  results  in  many  of  the  females  being  eaten  by  birds  or 
being  destroyed  because  of  rain.  cold,  or  failure  to  find  the  object  of 
their  quest.  A  few  moths  will  always  succeed  in  their  search,  but  the 
successful  proportion  will  be  greatly  decreased  by  persistent  crop 
rotation. 

Another  remedy,  probably  the  best  for  this  insect,  is  the  thorough 
destruction,  some  time  before  the  period  of  emergence  of  the  moths 
in  the  spring,  of  all  the  stalks  and  stubble  remaining  in  the  field  from 
the  preceding  crop.  If  all  this  trash  can  be  disposed  of  before  the 
opening  of  spring,  the  numbers  of  the  pest  must  be  greatly  diminished 
if  not  almost  exterminated,  for  the  only  form  in  which  the  insect 
passes  the  winter  is  that  of  the  caterpillar,  and  the  only  known  loca- 
tion is  in  the  lower  tip  of  the  corn  root,  snugly  hidden.  Some  few 
may,  however,  be  found  to  survive  in  the  roots  of  the  larger  grasses 
mentioned  above,  and  care  should  be  taken  in  such  cases  to  treat  these 
in  the  same  way.  The  method  employed  in  disposing  of  the  stubble 
and  stalks  will  depend  largely  on  the  conditions  in  individual  cases. 
If  the  stubble  is  cut  low  and  the  land  is  moderately  heavy,  a 
thorough  deep  plowing  may  suffice,  an  inch  or  two  of  well-settled  soil 
being  sufficient  to  prevent  the  escape  of  the  adult  moths.  Bringing 
the  stubble  to  the  surface  where  it  can  dry  will  kill  some  of  the  con- 
tained larva?,  but  this  method  depends  too  much  on  the  state  of  the 
weather  to  be  trusted.  By  far  the  most  effective  plan  is  to  remove 
the  stubble  from  the  field  with  a  rake  and  burn  it. 

In  the  cane  field  the  methods  of  treatment  must  be  adjusted  to 
correspond  with  the  methods  of  handling  that  crop.  The  larvae  com- 
monly spend  the  winter  in  the  trimmings  and  tops  which  have  been 
discarded  at  harvest  time  because  of  immaturity.  This  refuse,  left 
on  the  ground  throughout  the  winter,  becomes  dry  and  inflammable 
and,  if  thoroughly  burned  before  spring,  enough  larva'  will  be  killed 
to  insure  at  least  temporary  relief  from  the  ravage-  of  the  bore:". 

Any  method  which  will  insure  the  complete  destruction  of  the  over- 
wintering larva",  if  persisted  in  and  carried  out  simultaneously  over 
large  sections  of  the  country,  will  effectually  preclude  serious  damage 
from  the  insect. 

jImes  Wilson,  1/vOlJlV 

Secretary  of  Agriculture. 

Washington,  D.  C,  December  14,  1909. 

[Cir.  116] 

n 

UNIVERSITY  OF  FLORIDA 


3    1262    05252    3270 


